Recent rapid development of the biotechnology expands a demand of a flow cytometer and a cell sorter which are more commonly used in the various fields of medicine and biology for automatic analysis and fractionation of multiple cells. In general, the flow cytometer forms a stream of a sheath flow containing various cell particles in line, which are collected from a living body (blood, etc.) and dyed with a fluorescent labeling reagent, and emits laser beam onto the stream of the cell particles to detect light excited by and/or scattered at the cell particles (i.e., forward-scattered light, and side-scattered light, and multicolor fluorescence varying based on the fluorescent labeling reagent used) so that each of the cell particles in the stream is analyzed based upon the detected light In general, the flow cytometer converts the detected light having identification information of the cell particles into electrical signals, so as to statistically evaluate electrical signals for a mass of the cells collected from the sample, thereby allowing diagnosis of a health condition such as a disease of the living body. Further, the cell sorter also uses the electrical signals having identification information to selectively charge droplets containing a particular group of the cells to be sorted, and applying a DC electric field across a dropping path of the droplets, thereby selectively retrieving or sorting the desired cells.
FIG. 1 is a schematic view of the cell sorter 1, illustrating a general framework thereof. In general, the cell sorter 1 includes a fluid flow mechanism 10, an optical mechanism 40, and a sorting mechanism 60. The fluid flow mechanism 10 forms a stream of a sheath flow containing various cell particles, which are collected from a living body and dyed with a fluorescent labeling reagent. The optical mechanism 40 emits laser beams having different wavelengths onto each of the cell particles to detect scattering light and fluorescence. The sorting mechanism 60 analyzes electrical signals obtained from scattering light and fluorescence to sort the cell particles in the sample by providing the droplet containing the desired cell particles with electric charge at a given timing.
More particularly, as shown in FIG. 1, the fluid flow mechanism 10 includes a cylindrical flow chamber 12 defining a sheath flow, a sample container 14 for receiving suspension liquid containing fluorescently-labeled cell or biological particles, and a sheath container 16 for receiving a sheath liquid. Also, the fluid flow mechanism 10 includes a pressure controller 18 for controlling atmospheric pressure within the sample container 14, a plenum container 24 for storing a volume of the sheath liquid and supplying it to the sheath container 16, and air pumps 26, 27 for supplying compressed air to the sample container 14 and a plenum container 24, respectively. Provided downstream (below) the flow chamber 12 is a flow cell 30 having a cross section smaller than the flow chamber 12. In the fluid flow mechanism 10 so structured, upon activation of the air pumps 26, 27, the sample suspension liquid received within the sample container 14 and the sheath liquid received within the sheath container 16 are delivered to the flow chamber 12, to define a cylindrical laminar flow or sheath flow which encompasses the sample suspension liquid with the sheath liquid. Then, the sheath flow is ejected from an orifice on the bottom of the flow-path block 28 as a jet flow, and eventually, a series of discrete droplets D are separated from the jet flow at the break-off point BP when the flow cell 30 is applied with oscillation having a predetermined frequency.
The optical mechanism 40 emits a plurality of excitation laser beams having different wavelengths onto each of the cell particles running one-by-one in a line through the jet flow, and detects the forward- and side-scattered lights scattered at the cells and a variety of fluorescences having different wavelengths excited at the cells to output the identification information thereof to the sorting mechanism 60.
The sorting mechanism 60 identifies a type of each of the cell particles based upon the identification information of the cell particles, and uses an electrode positioned beneath the flow cell 30 to provide the cell particle at the break-off point BP with electric charge of polarity selected in accordance with the identification information, so that the droplets containing the charged cell particles are deflected on the dropping path between a pair of deflectors 62 having a given electrical potential difference, and are sorted into one of targeted slide glasses.
According to Patent Document 1 (Japanese Patent Publication 2005-315799, of which US counterpart is U.S. Pat. No. 7,417,734) commonly assigned to the applicant of the present application, which is incorporated herein by reference into the present application, the cell particles moving through the flow cell 30 are assumed to run along the center of the flow cell 30 at an uniform speed regardless of the cell particles. Thus, the sorting mechanism 60 of Patent Document 1 is designed to charge the cell particle that is assumedly located at the break-off point BP, at a fixed timing irrespective of the moving speed thereof.